Method for controlled removal of material from a solid surface

ABSTRACT

A catalytic method and an apparatus for selectively removing material from a solid substrate is provided. The method comprises contacting a surface of a solid substrate with a catalyst material in the presence of a reactant under conditions effective to selectively remove material from those areas of said solid substrate in contact with said catalyst material and said reactant.

FIELD OF THE INVENTION

The present invention relates broadly to microelectronics,micromachinery or optics and, in particular, to a geometricallycontrolled catalytic method wherein removal of material from a solidsubstrate is carried out without the need of using conventionalphotolithographic processes. The geometrically controlled catalyticremoval method of the present invention is particularly useful inproviding a pattern such as a deep trench capacitor and a shallow trenchisolation region to a semiconductor substrate in a single processingstep. In prior art processes, multiple photolithographic and etchingsteps are required to produce such a pattern in a semiconductorsubstrate. Additionally, complex shapes may be formed, possiblyproviding design advantages over the simple geometries of currentphotolithography/etch processes.

BACKGROUND OF THE INVENTION

In the field of semiconductor manufacturing, it is well known that apattern can be formed in a surface of a solid substrate by utilizingconventional photolithographic techniques. Conventionalphotolithographic processes include the steps of providing a photoresistor mask to predetermined areas of a solid substrate, patterning saidphotoresist or mask, etching the exposed areas of the solid substrateand stripping of the photoresist or mask. In such prior art processes,etching of the solid substrate is generally achieved by employing eithera wet etch or a dry etch.

Wet etching is carried out using a chemical etchant which is highlyselective for the particular solid substrate being etched. A majorproblem with wet etching is that an undercut often times develops oneach edge of the photoresist. This property of undercutting thephotoresist makes it impossible to achieve sub-tenth micrometer geometryreproducibly. Moreover, in order to etch a pattern into a solidsubstrate having multiple depths, repeated wet etching steps arerequired.

In the case of dry etching, ion beam etching (IBE) and reactive ionetching (RIE) are known in the art. These dry etching techniques areboth line-of-sight etching processes and are able to produce higherresolution patterns with tighter dimensional control. Despite this, eachof these dry etching techniques suffer from unique problems.

A major problem associated with IBE is that the edges of all features ofthe photoresist are etched at a faster rate due to a high flux ofincident ions. This phenomenon is caused by the reflection of bombardingions off the side walls of the photoresist. The above propertyassociated with IBE is referred to in the art as "trenching" and ittypically causes roughening at the edges of the etched features.

The problem generally encountered using RIE is the formation of tall,narrow pedestals of unetched material at the bottom of the patternfeature. This phenomenon which is referred to in the art as "grassing"is caused by localized masking of the photoresist during RIE. Suchpedestals may be removed by utilizing a wet etch process.

In view of the drawbacks mentioned hereinabove, prior art etchingprocesses (dry and wet etching alike) are incapable of providinggeometrically controlled removal of material from a solid substrate.Moreover, multiple etching steps are generally required to produce apattern in a solid substrate that has varying depths. Additionally, manycomplex geometries, such as curved or angled surfaces, are difficult oreven impossible to create using existing prior art methods. Thus, thereremains a need for developing a method for providing geometricallycontrolled removal of material from a solid substrate whereby patterningof the solid substrate is achieved without using prior artphotolithographic processes. Moreover, there is also a need fordeveloping a method wherein a pattern having different depths isproduced in a solid substrate utilizing a single step replacing themultiple photolithographic steps required by the prior art to obtain thesame pattern.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method ofselectively removing material from a solid substrate wherein a patternor planarized surface is produced.

Another object of the present invention is to provide a geometricallycontrolled removal method that is a replacement for prior art etching orplanarization methods and which overcomes all of the aforementionedproblems associated with such prior art techniques.

A further object of the present is to provide a catalytically inducedmethod which is highly effective in removing material from a solidsubstrate to form a desired three-dimensional or planar pattern in thesolid substrate.

These as well as other objects are achieved by the method of the presentinvention wherein a geometrically controlled pattern is formed in asolid substrate utilizing a catalyst material and a reactant.Specifically, the method of the present invention comprises contacting asurface of a solid substrate with a catalyst material in the presence ofa reactant under conditions effective to remove material from thoseareas of said solid substrate in contact with said catalyst material andsaid reactant, wherein at least one of said catalyst material or saidreactant is a solid.

In accordance with a preferred embodiment of the present invention,silicon or SiO₂ represent the solid substrate, W is the catalystmaterial and fluorine atoms represent the reactant.

As stated above, the instant invention utilizes a catalyst material anda reactant to effectively and selectively remove material from a solidsubstrate. Generally, the catalyst material is a solid and the productof the reaction between the reactant and the solid substrate is mobile,i.e. gas or liquid, thereby facilitating the removal of areas of saidsolid substrate in contact with said catalyst material and saidreactant. It is noted that since two of the species in the catalyticreaction are solids, the catalytic reaction of the present inventionoccurs only in those areas wherein the two solids are in contact. Nosufficient removal of material from the solid substrate occurs in areaswhich do not contain either the reactant or catalyst material. Areaction between the reactant and solid substrate may proceed withoutthe catalyst material, but it is slow and thus would not result in anysignificant removal of material from the solid substrate using theconditions employed in the present invention.

Another aspect of the present invention relates to an apparatus for thecontrolled removal of material from a solid substrate. In accordancewith this aspect of the present invention, the apparatus comprises: acatalyst material; a reactant; a solid substrate; and a means forcontacting said catalyst material with said solid substrate in thepresence of said reactant.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-1(b) are cross-sectional views illustrating one of thecatalytic induced removal methods of the present invention: (a) prior tocontacting, and (b) after contacting with a non-supported solid catalystmaterial.

FIG. 2 is a cross-sectional view of an alternate embodiment of thepresent invention wherein the catalyst material is supported on an inertsupport material.

FIG. 3 is a cross-sectional view of another alternate embodiment of thepresent invention wherein isolated catalyst particles are brought intocontact with a surface of a solid substrate.

FIGS. 4(a)-4(b) are cross-sectional views of a solid substrate having ametal layer deposited on the substrate: (a) prior to contacting with acatalyst material and a reactant; and (b) after contacting with acatalyst material and a reactant.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention which provides a method and an apparatus forgeometrically controlled catalytic removal of material from a solidsubstrate will now be described in more detail with reference to theaccompanying drawings wherein like reference numerals are used for likeand corresponding elements of the drawings. It is noted that each of theaccompanying drawings represent various embodiments of the presentinvention which will be described in greater detail hereinbelow.

In all these embodiments, a solid catalyst material and a mobilereactant (liquid or gas) are used to selectively remove portions of asolid substrate that are in contact with said solid catalyst materialand said mobile reactant. The result is the transfer of thethree-dimensional shape of the solid catalyst material to the solidsubstrate.

Referring first to FIGS. 1(a)-(b), there are shown the first embodimentof the present invention wherein the instant method is used to provide asemiconductor material having a deep trench capacitor region and ashallower trench isolation region. Specifically, in FIG. 1(a), there isshown a catalyst material 12 containing a preformed three-dimensionalpattern on one of its surfaces and a solid substrate 14 having a surface16.

The solid substrates employed in the present invention are materialswhich can be catalytically removed using a catalyst material and areactant. Suitable solid substrates which can be employed in the presentinvention include: semiconductor materials such as silicon, germanium,gallium, arsenic, indium and mixtures thereof, and dielectric materialssuch as SiO₂, diamond, Si₃ N₄, diamond-like carbon, fluorinated oxides,aerogels, polymers and the like. Also contemplated are other dielectricsthat have a resistivity value lower than SiO₂. Highly preferredmaterials for solid substrate 14 are silicon and SiO₂.

Catalyst material 12 contains at least one metal selected from GroupIVB, VB, VIB, VIIB and VIII of the Periodic Table of Elements (CASversion). Illustrative examples of such metals that can be employed inthe present invention include: Ti, Zr, Hf, V, Ta, Cr, Mo, W, Mn, Fe, Co,Ni, Ru, Rh, Pd and the like. Mixtures or alloys of these metals are alsocontemplated herein. A highly preferred metal employed in the presentinvention is W.

In accordance with the present invention, catalyst material 12 may beunsupported (as shown in FIG. 1(a)), supported (as shown in FIG. 2) orused as isolated particles (as shown in FIG. 3).

When supported, catalyst material 12 is supported on an inert supportmaterial 18. Suitable inert support materials employed in the presentinvention include, but are not limited to: glass, inert metals and inertpolymers. A highly preferred inert support material employed in thepresent invention is glass.

The catalyst material may be preformed in the desired three dimensionalpattern, or it can be deposited onto an inert support materialcontaining the desired three-dimensional pattern using conventionalmeans well known to those skilled in the art. For example, the desiredpattern can be formed by chemical vapor deposition, sputtering and likethereof. In one embodiment of the present invention, the geometry of thecatalyst material may be a flat plane, thereby planarizing the surfaceof the solid substrate it comes in contact with. This embodiment mayprovide a useful alternative to chemical-mechanical polishing (CMP) orother planarization techniques.

In accordance with the present invention, surface 16 of solid substrate14 is brought into contact with the patterned surface of catalystmaterial 12 in the presence of a reactant under conditions effective toselectively remove those areas of the surface of the solid substrate incontact with the catalyst material and the reactant.

The term "reactant" is used herein to denote a solid, liquid or gaseousetchant material. The term "mobile reactant" is used herein to denote aliquid or gaseous etchant material. Suitable etchants include chlorineatoms, oxygen atoms, fluorine atoms and the like. Mixtures of theseatoms are also contemplated herein. A highly preferred reactant employedin the instant invention is fluorine atoms which are derived from WF₆gas. It is noted that when the reactant is a solid, the catalystmaterial may be a liquid or gas. That aspect of the present inventionwill be discussed in greater detail hereinbelow.

The conditions employed in the present invention to effectively removeportions of the solid substrate may vary over a wide range, butgenerally the conditions are as follows: Temperature is from about 350°to about 450° C., pressure is from about 0.5 to about 1 psig, time isfrom about 1 to about 20 seconds; and reactant partial pressure is fromabout 0.005 to about 0.01 psig.

After carrying out the contacting step in the above described manner, ageometrically etched pattern is formed in the surface of the solidsubstrate. Specifically, as is shown in FIG. 1(b), solid substrate 14having a deep trench region 20 and a shallower trench region 22 isformed utilizing the single reaction step of the present invention.Other structures containing a number of different three-dimensionalpatterns having varying depths and configurations can be formed by themethod of the present invention. As stated above, the present methodrepresents a viable replacement for conventional lithographic processes.

Referring again to FIG. 2, there is shown a second embodiment of thepresent invention wherein catalyst material 12 is supported on an inertsupport material 18. In this figure, the catalytic template includesisolated catalyst material 12, 12' and 12" respectively, on inertsupport material 18. When such a template is used in the method of thepresent invention, the removal process does not occur in those areaswherein the catalyst material is not present on the inert supportmaterial. The reaction conditions using this aspect of the presentinvention are the same as those mentioned hereinabove. In addition tothe embodiment shown in FIG. 2, the catalyst material may be supportedover the entire surface of inert support material 18 that has athree-dimensional pattern.

FIG. 3 shows another embodiment of the present invention whereinisolated catalyst particles 26 and 26" are used to create wormholes ormoleholes in solid substrate 14. The catalyst particles contain the samemetals as described for catalyst material 12. Again, material from solidsubstrate 14 is removed only in those areas wherein the catalystparticles and the reactant come in contact with the surface of solidsubstrate 14. No removal of material occurs in areas wherein thecatalyst particles are not present.

As is known to those skilled in the art wormholes are very smalldiameter tubes (hundreds of Å extending up to microns) formed through asolid material such as silicon. Moleholes are different from wormholesin that they have a much larger diameter which is in the order of about0.05 to about 0.5 micrometers. In both of these defects, a particle isobserved to be present at the end of the tube. In the case of wormholes,the particle is usually W, whereas in moleholes the particle is atitanium silicide agglomerate.

FIGS. 4(a)-(b) illustrate a planarization embodiment of the presentinvention. In FIG. 4(a), solid substrate 14 has a metal layer 28deposited thereon. Preferred metals for layer 28 are W or Cu. FIG. 4(a)represents a structure prior to contact with said catalyst material andsaid reactant, whereas FIG. 4(b) represents the structure after contactwith said catalyst material and said reactant. As shown in thesefigures, the present invention can be used as an alternative tochemical-mechanical polishing. Specifically, the method of the presentinvention can be used to planarize metal layer 28 providing thestructure shown in FIG. 4(b). In this embodiment, metal layer 28 isremoved using a catalyst material having a planarized surface.

Although the invention has been described as using a solid catalystmaterial, it is also possible that the catalyst material is mobile, i.e.a liquid or a gas. When a mobile gas or liquid is employed as thecatalyst material, the reactant is in solid form and is shaped inaccordance with the desired three-dimensional pattern to be formed inthe solid substrate. Such a template would result in different shapesbecause the solid reactant would be consumed resulting in structures ofdecreasing dimension as depth increases. This embodiment would also meanthat the etchant template could only be used a number of times before itis completely consumed. When this embodiment is employed, the removal ofmaterial from the solid substrate still occurs in areas wherein thesolid substrate is in contact with the mobile catalyst and the solidreactant.

When the catalyst material is mobile and the reactant is a solid, theconditions employed to selectively remove areas of the solid substrateare the same as those mentioned hereinabove.

In accordance with another aspect of the present invention, an apparatusincluding a surface of a solid substrate, a catalyst material and areactant is also provided. Specifically, the apparatus of the presentinvention includes means for contacting the surface of said solidsubstrate with said catalyst material in the presence of said reactant.An illustrative example of a specific means for contacting said solidsubstrate and said catalyst material is by utilizing a piezoelectronicpositioner. Other means for said contacting include a robot arm, a vise,and the like.

As stated above, the method of the present invention provides ageometrically controlled means for forming a desired pattern in a solidsubstrate. The pattern is formed without the need of using conventionalphotolithographic techniques. Thus, the present invention represents asignificant advancement in the field of microelectronics. Moreover,patterns having varying depths in a solid substrate can be achieved in asingle step when the method of the present invention is employed. Inaddition, patterns having complex shapes, such as curves and angledsurfaces, may be produced. Moreover, the catalyst material may have aplanar configuration which, when employed in the present invention,would planarize the solid substrate, or provide for blanket removal ofthe solid substrate material.

While the invention has been particularly described with respect topreferred embodiments thereof, it will be understood by those skilled inthe art that the foregoing and other changes in form and detail may bemade without departing from the scope and spirit of the invention.

Having thus described my invention, what I claim as new, and desire tosecure by the Letters Patent is:
 1. A method for geometricallycontrolled removal of material from a solid substrate,comprising:contacting a surface of a solid substrate with a solid,separately supported catalyst material, said catalyst material having ageometrical pattern on one of its surfaces, in the presence of areactant under conditions effective to remove those areas of said solidsubstrate in contact with said catalyst material and said reactantthereby transferring the geometrical pattern to said solid substrate,wherein said solid substrate does not contain a photoresist thereon. 2.The method of claim 1 wherein said solid substrate comprises asemiconductor material or a dielectric material.
 3. The method of claim2 wherein said solid substrate is a semiconductor material selected fromthe group consisting of silicon, germanium, gallium, indium, arsenic andmixtures thereof.
 4. The method of claim 3 wherein said solid substrateis silicon.
 5. The method of claim 2 wherein said solid substrate is adielectric material selected from the group consisting of SiO₂, diamond,Si₃ N₄, diamond-like carbon, fluorinated oxides, arogels, polymers andother dielectric materials.
 6. The method of claim 5 wherein said solidsubstrate is SiO₂.
 7. The method of claim 1 wherein said catalystmaterial comprises at least one metal selected from Group IVB, VB, VIB,VIIB and VIII of the Periodic Table of Elements.
 8. The method of claim7 wherein said metal is tungsten.
 9. The method of claim 1 wherein saidgeometrical pattern is a plane.
 10. The method of claim 1 wherein saidsupport is an inert support material selected from the group consistingof glass, inert metals and polymers.
 11. The method of claim 10 whereinsaid inert support material is glass.
 12. The method of claim 1 whereinsaid reactant is a liquid or gas.
 13. The method of claim 12 whereinsaid reactant is a gas.
 14. The method claim 12 wherein said reactantcomprises chlorine atoms, oxygen-atoms, fluorine atoms or mixturesthereof.
 15. The method of claim 14 wherein said reactant comprisesfluorine atoms.
 16. The method of claim 1 wherein said contacting iscarried out at a temperature of about 350° to about 450° C., a pressureof about 0.5 to about 1 psig for a time period of about 1 to about 20seconds using a reactant partial pressure of about 0.005 to about 0.01psig.
 17. The method of claim 1 wherein said solid substrate is silicon,said catalyst material is solid tungsten, and said reactant is a gascomprising fluorine atoms.
 18. The method of claim 17 wherein saidtungsten is supported on glass.
 19. The method of claim 1 wherein saidsolid substrate is SiO₂, said catalyst mate rial is solid tungsten andsaid reactant is a gas comprising fluorine atoms.
 20. The method ofclaim 19 wherein said tungsten is supported on glass.
 21. The method ofclaim 1 wherein said solid substrate comprises silicon, said catalystmaterial is solid tungsten particles and said reactant is a gascomprising fluorine atoms.
 22. A method for the geometrically controlledremoval of material from a solid substrate, comprising:contacting asurface of a solid substrate with a catalyst material in the presence ofa solid reactant, said solid reactant having a geometrical pattern onone of its surfaces, under conditions effective to remove those areas ofsaid solid substrate in contact with said catalyst material and saidreactant thereby transferring the geometrical pattern to said solidsubstrate, wherein said solid substrate does not contain a photoresistthereon.
 23. The method of claim 22 wherein said catalyst material is aliquid or gas.
 24. The method of claim 1 wherein said catalyst materialcomprises catalyst particles supported on an inert support material. 25.The method of claim 1 wherein said solid substrate includes a metallayer deposited on one of its surfaces.
 26. The method of claim 25wherein said metal layer is comprised of W or Cu.